It is known to use glitter as a decoration in a variety of environments. Glitter, for example, has been used as a pigment for paint and liquid glue as well as in some goldleafing. Glitter was originally made only of small particles of a base metal, including gold, silver, and aluminum. In recent years, however, glitter has been made of a polyester film having a dye coat on one side and a metalized aluminum layer covered by a second dye coat on the other. The metalized coating is typically vacuum deposited, and the colored layer can comprise a dye colored epoxy.
Metal glitter used in paint was often subject to degradation by acids or bases in the liquid paint. This degradation significantly reduced the brightness of the glitter in many cases.
Metal glitter has not been included in hot melt adhesive compositions for several reasons. Metal glitter in these compositions is subject to degradation by acid tackifiers in the adhesive. Metal glitter is also very abrasive and causes unacceptable physical wear on the high shear mixers and extruders used in the manufacture of hot melt adhesives. This wear caused by the metal glitter is significant even though the equipment is often made of hardened materials because of the close tolerances required in the equipment and the reduction in efficiency when these tolerances are not met. A further disadvantage of metal glitter is that it has a high specific gravity compared to that of the adhesive composition. Thus, metal glitter tends to settle to the bottom of containers.
Polyester based glitter, on the other hand, is advantageous in that it is not subject to degradation by the tackifiers and does not cause wear on the manufacturing equipment or on the melt chamber of the glue gun itself. This is because the epoxy coating on the one side and the polyester on the other protect the metal. Moreover, the specific gravity of polyester glitter is about that of the adhesive composition, whereby polyester glitters remain suspended in the adhesive composition or settle at a low rate.
Polyester glitter, however, does suffer from the disadvantage that it is degraded by the temperatures normally required by hot melt adhesives. Normal hot melt adhesives require temperatures in the range of 380.degree. F. to 400.degree. F., and exposure to such temperatures for even as long as several minutes damages the polyester substrate and destroys the reflective film.
Accordingly, it has heretofore been the belief in this art that it is not possible to provide decorative glitter in hot melt adhesives.